Insect repellent

  An insect repellent is a substance applied to skin, clothing, or other surfaces which discourages insects (and arthropods in general) from landing or climbing on that surface. There are also insect repellent products available based on sound production, particularly ultrasound (inaudibly high frequency sounds). These electronic devices have been shown to have no effect as a pest repellent by studies done by the EPA and many universities.^[1]

Insect repellents help prevent and control the outbreak of insect-borne diseases such as malaria, Lyme disease, Dengue fever, bubonic plague, and West Nile fever. Pest animals commonly serving as vectors for disease include the insects flea, fly, and mosquito; and the arachnid tick.

Common insect repellents include:

• DEET (N,N-diethyl-m-toluamide)
• Essential oil of the lemon eucalyptus and its active ingredient p-menthane-3,8-diol (PMD)
• Icaridin, also known as picaridin, Bayrepel, and KBR 3023
• Citronella oil
• Permethrin
• Soybean oil^[2]
• Neem oil

Usually insect repellents work instead by masking human scent, or by using a scent which insects naturally avoid.^{[citation needed]} Permethrin is different in that it is actually a contact insecticide.

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Repellent effectiveness

Synthetic repellents tend to be more effective than 'natural' repellents.^[3][4][2] However, some plant-based repellents are comparable to, or somewhat better than synthetics - depending on the formula.^{[5] [3][6]} Essential oil repellents tend to being short-lived in their effectiveness due to their volatile nature.

A test of various insect repellents by an independent consumer organization found that repellents containing DEET or picaridin are more effective than repellents with ‘natural’ active ingredients. All the synthetics gave almost 100% repellency for the first 2 hours, where the natural repellent products were most effective for the first 30-60 minutes, and required reapplication to be effective over several hours.^[7]

For protection against mosquitos, the U.S. Centers for Disease Control recommend DEET, icaridin, or oil of lemon eucalyptus for skin, and permethrin for clothing, gear, or bed nets.^[8] Oil of lemon eucalyptus was found to be more effective than other plant-based treatments, and had similar effectiveness to low concentrations of DEET. ^[9] However, research found that neem oil is mosquito repellent for up to 12 hours.^[10] Citronella oils mosquito repellency has also been verified by research,^[11] including effectiveness in repelling Aedes aegypti, ^[12][13], but requires reapplication after 30-60 minutes.

Repellent safety

Regarding safety with insect repellent use on children and pregnant women:

• Children may be at greater risk for adverse reactions to repellents, in part, because their exposure may be greater.
• Keep repellents out of the reach of children.
• Do not allow children to apply repellents to themselves.
• Use only small amounts of repellent on children.
• Do not apply repellents to the hands of young children because this may result in accidental eye contact or ingestion.
• Try to reduce the use of repellents by dressing children in long sleeves and long pants tucked into boots or socks whenever possible. Use netting over strollers, playpens, etc.
• As with chemical exposures in general, pregnant women should take care to avoid exposures to repellents when practical, as the fetus may be vulnerable.

Regardless of which repellent product used, it is recommended that the label is read before use and directions carefully followed.^[14] Usage instructions for repellents vary from country to country. Some insect repellents are not recommended for use on younger children.^[9]

In the DEET Reregistration Eligibility Decision (RED) the EPA reported 14 to 46 cases of potential DEET associated seizures, including 4 deaths. The EPA states: " ..it does appear that some cases are likely related to DEET toxicity," but observed that with 30% of the US population using DEET, the likely seizure rate is only about one per 100 million users.^[15]

The Pesticide Information Project of Cooperative Extension Offices of Cornell University states that "Everglades National Park employees having extensive DEET exposure were more likely to have insomnia, mood disturbances and impaired cognitive function than were lesser exposed co-workers". ^[16]

The U. S. Environmental Protection Agency states that citronella oil shows little or no toxicity and has been used as a topical insect repellent for 60 years. However, the EPA also states that citronella may irritate skin and cause dermatitis in certain individuals.^[17] Canadian regulatory authorities concern with citronella based repellents is primarily based on data-gaps in toxicology, not on incidents.^{[18] [19]}

Naturally-occurring insect repellent

There are many naturally-occurring pesticides which can be used as an insect repellent and some of these are:

• Achillea alpina (Repels mosquitos)
• Basil^[20]
• Camphor
• Eucalyptus oil (eucalyptol, syn. cineol), mosquitos
• Garlic^[21]
• Lemongrass^[22]
• Lavender^[23][24]
• Marigolds
• Marjoram^[25]
• Neem oil
• Peppermint^[26]
• Rosemary^[25]
• Sage^[27]
• Tea tree^[28]

See also

• Mosquito control
• Mosquito net
• Pest control

References

• Iowa State University Study: Nepetalactone 10 times more effective than DEET

Notes